1. Field of Invention
The invention relates to an ink jet apparatus, an ink jet apparatus driving method, and a storage medium for storing an ink jet apparatus control program.
2. Description of Related Art
In conventional ink jet apparatuses, the volumetric capacity of an ink channel is changed by deformation of piezoelectric ceramic. When the volumetric capacity is reduced, ink in the ink channel is ejected as an ink droplet from a nozzle and, when the volumetric capacity is increased, ink flows into the ink channel from an ink guide port. In a printhead of this kind of ink jet apparatus, a plurality of ink channels are formed and separated by piezoelectric ceramic sidewalls. An ink supplying means, such as an ink cartridge, is connected to one end of each ink channel, and an ink ejection nozzle (hereinafter referred to as a nozzle) is provided for the other end of each ink channel. Selective reductions of the volumetric capacity of the ink channels by deformation of the sidewalls, according to print data, cause ink droplets to be ejected from the corresponding nozzles onto a print medium and, as a result, characters and graphics are printed thereon.
Ink jet apparatuses of this kind, i.e., drop-on-demand type ink jet heads which eject ink droplets for printing, are becoming widespread because of their excellent ejection efficiency and low running costs.
Conventionally, in this kind of the ink jet head, there has been a need to minimize the volume of an ink droplet to be ejected for high-quality printing, such as photographic printing. As one of the attempts to reduce the ink droplet, a driving method using an ejection pulse and a droplet reducing pulse has been adopted. After applying an ejection pulse to eject an ink droplet, a droplet reducing pulse is applied to retrieve a portion of the ink droplet, which is about to be ejected, into the ink channel.
However, in such a driving method, because pressure waves remaining in the ink channel are not suppressed, ejection of a minute ink droplet may become unstable or unwanted or no ink ejection may be caused when the ink jet head is driven at high printing frequencies and, as a result, print quality deteriorates.
In view of the forgoing problem, the invention provides an ink jet apparatus. an ink jet apparatus driving method, and a storage medium for storing an ink jet apparatus control program that ensure stable ejection of an ink droplet smaller than or equal to 20 pl (picoliters) to form a dot during printing at high frequencies and thereby achieve high-speed and high-quality printing.
According to one aspect of the invention, a method of driving an ink jet apparatus is provided. The ink jet apparatus includes a nozzle from which an ink droplet is ejected, an ink channel filled with ink and connected to the nozzle, an actuator that changes a volumetric capacity of the ink channel to generate a pressure wave in the ink channel, and a controller that applies an ejection pulse signal to the actuator to cause ink droplet ejection from the nozzle. By the ink jet apparatus driving method, which is applied when an ink droplet smaller than or equal to 20 pl in volume is ejected to form a dot, an ejection pulse signal having a first drive waveform or an ejection pulse signal having a second drive waveform is selectively used to form a dot. An ejection pulse signal having the first drive waveform is used when there are no ejection commands either immediately before or after a dot to be formed. The first drive waveform includes a first ejection pulse and an ink droplet reducing pulse for retrieving a portion of an ink droplet about to leave the nozzle. The first ejection pulse is equal in crest value to the ink droplet reducing pulse. Except when there are no ejection commands either immediately before or after the dot to be formed, an ejection pulse signal having the second drive waveform is used. The second drive waveform includes a second ejection pulse and an ejection stabilizing pulse for suppressing residual vibrations generated by the second ejection pulse. The second ejection pulse is equal in crest value to and shorter in pulse width than the first ejection pulse, and the ejection stabilizing pulse is equal in crest value to the first ejection pulse.
By this method, the second drive waveform having an ejection stabilizing pulse is used to eject an ink droplet smaller than or equal to 20 pl to form a dot in response to one of continuous print commands and/or during printing at high frequencies, and the first drive waveform having a droplet reducing pulse is used to eject an ink droplet smaller than or equal to 20 pl to form a dot in response to a discontinuous print command. Accordingly, an ink droplet smaller than or equal to 20 pl can be ejected stably during printing at high frequencies.
In this driving method, when T represents a one-way propagation time of a pressure wave along the ink channel, a pulse width of the first ejection pulse is substantially equal to T, a pulse width of the ink droplet reducing pulse is within a range of 0.2T to 0.3T, a time period between the first ejection pulse and the ink droplet reducing pulse is within a range of 0.4T to 0.6T, a pulse width of the second ejection pulse is within a range of 0.5T to 0.7T, a pulse width of the ejection. stabilizing pulse is within a range of 0.2T to 0.3T, and a time period between the second ejection pulse and the ejection stabilizing pulse is within a range of 2.0T to 2.2T.
By setting the pulse widths and the pulse applying timing in this way, differences between the first and second drive waveforms in ink droplet ejection velocity and volume are minimized. In addition, ejection stability is ensured in each printing condition to which the first or second drive waveform is applied.
According to another aspect of the invention, an ink jet apparatus that accomplishes the above-described method is provided. The ink jet apparatus includes a controller having a memory and an output device. The memory stores the first and second drive waveforms as ejection pulse signals, and the output device judges whether there are no ejection commands either immediately before or after a dot to be formed and, if so, applies an ejection pulse signal having the first drive waveform to the actuator and, if not so, applies an ejection pulse signal having the second drive waveform to the actuator.
According to still another aspect of the invention, a storage medium for storing a program that accomplishes the above-described method is provided. The program in the storage medium is loaded into a personal computer, or the like, from which print data is outputted to an ink jet apparatus to perform printing. The program accomplishes the function of generating first and second drive waveforms as ejection pulse signals, and the function of judging whether there are no ejection commands either immediately before or after a dot to be formed and, if so, applying an ejection pulse signal having the first drive waveform to the actuator and, if not so, applying an ejection pulse signal having the second drive waveform to the actuator.